Twelve roof penetrations on 8,000 square feet, and a facilities budget of $600 a month that stopped covering them somewhere around year three. Across ten years, a welded PVC roof with properly flashed curbs costs less than the patch callouts it replaces. Welded PVC Seams Change The Penetration MathReplacement changes what a penetration costs you. What I cannot pin down is how much low-slope roof failure in this region begins at penetrations versus at seams. Price the welded membrane once, then compare it honestly against what the patching is already costing you every year.